The present invention relates to a motor wheel for driving the driving wheel of an industrial vehicle and the like.
As it is known motor wheels for driving the driving wheel of an industrial vehicle, for example of the road-paver type, in some applications have a built-in two-speed gearbox which allows to obtain two different speeds, i.e., a low or working speed and a high or travel speed.
The motor wheel currently in use generally has a gearbox provided by means of a single-stage epicyclic assembly arranged upstream of a two-stage fixed-ring epicyclic assembly which is actuated by means of two hydraulic clutches, which in practice provide the two required operating speeds.
Generally speaking, when one clutch is actuated, motion is transferred directly from the input sun gear to the output carrier, thus obtaining a direct transmission which provides the direct speed, while when the other clutch is closed the ring gear of the epicyclic gear system is locked, providing a fourfold reduction ratio which corresponds to the low speed.
Both clutches are of the negative-actuation type, i.e., have a clutch which is normally closed by springs and is opened by a hydraulic pressure, so that when there is no actuation pressure the two clutches are both closed, providing the parking brake function.
This type of operating layout suffers some problems; in particular, the clutches are usually dimensioned for coupling when the machine is not moving, since it is not necessary to select the operating range while the machine is moving; however, the fact of having a drive operated by means of clutches which in practice do not clash, allows an improper use of said clutches while the machine is moving, accordingly leading to rapid wear/burnout of the clutches.
Moreover, providing the drive by means of clutches is a delicate and expensive approach with considerable mechanical complexities which introduce significant costs for functions which in practice are not necessary.
The aim of the present invention is to solve the above noted problem by providing a motor wheel for driving the driving wheel of an industrial vehicle and the like which allows to shift between the working speed and the transfer speed without having to resort to the use of two clutches but simply by providing a mechanical drive with hydraulic preselection which has a very low cost and simplifies not only manufacture but also its operation.
Within this aim, a particular object of the invention is to provide a motor wheel in which the flow-rate and the actuation pressure of the drive do not affect the operation of the gearbox, since they act only during preselection.
Another object of the present invention is to provide a motor wheel in which shifting can be requested regardless of the loading conditions of the gearbox, since if the gear system is subjected to torque, as a consequence of the shifting request, said gearbox remains set to the current speed until torque conditions occur which allow shifting to the preselected speed.
Still another object of the invention is to provide a motor wheel for driving the driving wheel of an industrial vehicle and the like which, by means of its particular constructive characteristics, is capable of giving the greatest assurances of reliability and safety in use.
These and other objects which will become better apparent are achieved by a motor wheel for driving the driving wheel of an industrial vehicle and the like, according to the invention, characterized in that it comprises, upstream of a two-stage rotary-ring reduction unit, a gearbox with fixed-ring epicyclic gear train, with at least two positions which respectively correspond to the high or travel speed and to the low or working speed, a parking brake being further provided downstream of said gearbox with respect to the motion input.